On-site power plant control including adaptive response to transient load requirements

ABSTRACT

An on-site power plant ( 24 ) has a controller ( 40 ) that selectively controls operation of prime movers ( 26, 28, 30 ). In one example, the controller ( 40 ) changes the number of operating prime movers responsive to a transient in a load ( 22 ) requirement while continuing to operate at least one of the prime movers. One example includes prioritizing the prime movers ( 26, 28, 30 ) for operation based upon the needs of a cogeneration unit ( 32, 34, 36 ) associated with the prime movers for providing a temperature control function within a facility. Another example includes controlling operation of the prime movers based upon a capacity for fueling the prime movers.

FIELD OF THE INVENTION

This invention generally relates to on-site power plants. Moreparticularly, this invention relates to controlling operation of thecomponents of an on-site power plant.

DESCRIPTION OF THE RELATED ART

On-site power plants are known. Typical arrangements include a pluralityof prime movers for generating power. Microturbines serve as the primemovers in some examples.

Most on-site power plants provide electrical power to a facility such asa building. Some on-site power plants provide thermal energy, electricalenergy and include temperature control functions to provide heating orcooling to a facility. Such arrangements typically include acogeneration unit that operates based upon exhaust from a microturbine.Depending on the need for heating or cooling within the facility, thecogeneration unit operates in a corresponding fashion, utilizing exhaustfrom the prime movers according to the arrangement of a particularsystem.

In some situations, on-site power plants include several groups of primemovers, each group being associated with a cogeneration unit. There arevarious challenges in controlling the operation of such on-site powerplants.

A primary concern for many installations is to avoid having the on-sitepower plant generate more power than that which is required by the loadto avoid power being exported to a grid associated with an externalpower source such as a utility company. Safety relays shut off anon-site power plant if the power exported to the grid exceeds a selectedthreshold, which may be power or time-dependent.

For example, an on-site power plant may be operating at a desired powerlevel when there is a rapid down transient in the amount of powerrequired by the load. To avoid having excess power exported to the grid,the typical solution is to shut down the entire on-site power plant.Under such a circumstance, the outside power source provides power tothe facility. That solution has drawbacks including potentially leavingthe facility without heating or cooling for some period of time, whichrequires incurring increased utility demand charges. Additionally, thelocally generated power from the on-site power plant may not be providedfor an extended period of time, which defeats the purpose of having theon-site power plant.

Another issue with existing arrangements is that the exhaust gas streamprovided to the cogeneration unit does not always correspond to thedemand for heating or cooling within the facility. In manycircumstances, there are efficiency losses because excess exhaust gasfrom the prime movers is vented to atmosphere, supplementary heaters orchillers are required to maintain a desired temperature within thefacility, or both. There are known building management systems that arecapable of determining which cogeneration unit of a group of unitsassociated with an on-site power plant would be best suited to provide arequired temperature in a facility. There has been no arrangement,however, that utilizes such information in controlling the prime moversof an on-site power plant.

Another issue associated with known arrangements is that the natural gasfuel provided to the prime movers typically must be processed (e.g.,through a booster). There are situations where one or more fuel boostersmay malfunction or be temporarily taken out of service for repair orroutine maintenance, for example. Under such circumstances, knownarrangements tend to shutdown the entire on-site power plant because theavailable capacity for fueling is not adequate for operating the primemovers that are running under such circumstances. Additionally, duringstart up of prime movers, high inlet gas pressures require higher fuelconsumption rates compared to normal operation. One attempt ataddressing this issue is to provide excess gas booster capacity forstarting the prime movers. This adds cost to a system, which isundesirable. There is a need for an improved control strategy foroperating prime movers based upon fuel gas availability.

This invention addresses the need for improved control over on-sitepower plant operation and avoids the various drawbacks mentioned above.

SUMMARY OF THE INVENTION

An exemplary method of controlling an on-site power plant that has aplurality of prime movers for generating power includes operating aplurality of the prime movers to generate a first level of power for aload. Operation of the prime movers is adjusted responsive to a downtransient in the load while continuing to operate at least one of theplurality of prime movers to generate a second, relatively lower levelof power for the load.

By maintaining at least one of the prime movers in operation, thedisclosed example avoids shutting down the entire on-site power plantresponsive to a down transient in the power requirements at a loadwhenever such continued operation is possible while avoiding trippingthe relay. This example provides the benefit of continuing to realizethe advantage of having an on-site power plant while also avoidingexporting power to a grid in a manner that would otherwise result inshutdown of the on-site power plant by tripping a reverse powerprotective relay.

One example includes determining a capacity for fueling the on-sitepower plant based upon an operating condition of a fuel gas booster, forexample. The determined capacity is then used to determine how tocontrol the prime movers such as selecting an appropriate number ofprime movers for operation. By controlling which of the prime moversoperates responsive to available fuel capacity, the disclosed exampleavoids shutdowns of the on-site power plant that are otherwiseassociated with unmatched fuel consumption and fuel supply capacity.

Another example includes prioritizing which of the prime movers will beused responsive to a determination regarding a temperature controlrequirement. In one example, a determination is made regarding whichcogeneration unit will best provide the needed temperature control. Adecision is then made regarding which prime mover to operate to ensurethat the determined cogeneration unit receives an exhaust stream forproviding the desired temperature control. One example includesoperating at least one prime mover at full capacity to obtain the bestpossible efficiency in power generation and in operation of thecogeneration unit.

A disclosed example combines each of the techniques mentioned above sothat the power output from the on-site power plant corresponds to thepower required at a load without exceeding the required power,corresponds to the available fuel capacity and controls operation of theprime movers so that fuel consumption does not exceed the availablecapacity, and ensures that a preferred cogeneration unit receives asmuch prime mover exhaust as possible to meet a temperature controlrequirement.

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an on-site power plant arrangementdesigned according to an example embodiment of this invention.

FIG. 2 is a flowchart diagram summarizing one example control strategy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows a system 20 for providing power to a facilitysuch as a building. The facility is schematically shown as an electricalload 22 and a thermal load 23 in the illustration. An on-site powerplant 24 includes components arranged in a known manner for generatingpower for use by the electrical load 22 and to provide temperaturecontrol for the thermal load 23. In the illustrated example, the on-sitepower plant 24 includes a plurality of prime movers for generatingpower. In one example, the prime movers comprise microturbines.

In the illustrated example, the prime movers are grouped such that thereare a first plurality of prime movers 26, a second plurality of primemovers 28 and a third plurality of prime movers 30. Each plurality ofprime movers is associated with a cogeneration unit in a known manner.The cogeneration unit 32 is associated with the plurality of primemovers 26. Another cogeneration unit 34 is associated with the primemovers 28 while a third example cogeneration unit 36 is associated withthe prime movers 30. As known, a cogeneration unit receives the exhauststream on a selective basis from the prime movers associated with it.For example, the exhaust stream from the prime movers 26 is provided tothe cogeneration unit 32 on a selected basis but not to the cogenerationunits 34 or 36. Similarly, the exhaust stream from the prime movers 30is supplied to the cogeneration unit 36 on a selective basis but not tothe cogeneration units 32 or 34.

The illustrated example includes a controller 40 that controls operationof the prime movers. The example controller 40 utilizes informationregarding various aspects of the requirements at the load 22, the load23 or both, for selectively controlling operation of the prime movers ofthe on-site power plant 24. The example controller 40 has severalcapabilities that may be used individually or collectively to meet theneeds of a particular situation. Given this description, those skilledin the art will realize what aspects of the example controller 40 willbe useful in their situation. One controller is schematically shown fordiscussion purposes. Those who have the benefit of this description willbe able to select one or more processors or to design appropriatehardware, software, firmware or a combination of them to realize acontroller that meets the needs of their particular situation.

FIG. 2 includes a flow chart diagram 42 that illustrates one examplecontrol strategy. That includes various features of the examplecontroller 40. Some example embodiments will not necessarily includeevery step schematically shown in FIG. 2. The flow chart 42 begins at 44where the controller 40 determines the required power for the load 22.In the example of FIG. 1, the load 22 receives power from the on-sitepower plant 24 and an external source of power 46, such as a utilitycompany. In the illustrated example, the controller 40 determines howmuch power is provided to the load by the outside power source or grid46 through a conventional meter 48. The controller 40 also knows howmuch power is provided to the load 22 from the on-site power plant 24because the controller 40 knows how many of the prime movers arecommanded to operate at a given time. The controller determines theamount of power based on at least one of an indication of prime moverstatus from a suitable sensor, an estimate of power output levelsdeveloped by engineers, or both.

In FIG. 2, at 50, the controller 40 determines the number of primemovers required to provide the desired power for the load 22. In someexamples, the controller 40 seeks to maximize the amount of powerprovided to the load 22 from the on-site power plant 24 to minimize theamount of power required from the grid 46. At the same time, thecontroller 40 seeks to avoid having the on-site power plant 24 produceany excess power not absorbed by the load 22 to avoid exporting power tothe grid 46. As known, utility companies require protective relays thatprevent power export from the on-site power plant 24 to the grid 46.Exporting power to a grid usually results in tripping a relay (notillustrated) that results in shutting down the on-site power plant 24.This is undesirable, in part, because resetting the relay istime-consuming and costly. The controller 40 monitors the power outputof the on-site power plant 24 and selectively controls operation of theprime movers to avoid such situations.

In FIG. 2, at 52, the controller 40 determines whether the number ofprime movers currently operating is greater than that required to meetthe power requirements at the load 22. If the amount of power generatedby the on-site power plant 24 is within the amount required by the load22, the controller 40 continues at 54 to determine whether there isenough fuel for operating that number of prime movers.

As schematically shown in FIG. 1, a fuel booster arrangement 56 includesone or more known fuel booster devices. The fuel booster arrangement 56provides fuel such as gas from a fuel supply 58 to the prime moverswithin the on-site power plant 24. The example controller 40 determinesthe operating condition of the fuel booster arrangement 56 to make adetermination regarding the capacity for fueling the prime movers. Inthe event that one or more of the fuel boosters is malfunctioning or hasbeen removed from service, the controller 40 may reset the number ofprime movers to be operated to maintain that number within the availablecapacity. This is shown for example in FIG. 2 at 60. In one example, thecontroller 40 determines how many prime movers may operate at fullcapacity based upon a given fuel booster capacity. The controller 40then selects the maximum number of prime movers that can operate at fullcapacity given the determined capacity.

Another example includes controlling operation of the prime movers in amanner that is based upon the available fuel booster capacity. Forexample, microturbine prime movers do not require as much pressure anddo not have as high a fuel consumption rate during normal operationcompared to start up. The controller 40, therefore, in one example,avoids simultaneously starting up the prime movers. Staggering the starttimes of the prime movers helps to even out the fuel consumption rate tokeep it within the capacity provided by the available, operating fuelboosters within the fuel booster assembly 56. One advantage to thisexample arrangement is that the controller 40 avoids having the on-sitepower plant 24 shutdown because of inadequate fuel supply capacity foroperating the desired number of prime movers at a given time. Some knownsystems tend to shutdown the entire system when fuel supply isinadequate to meet a demand of the prime movers that are supposed to becurrently operating. The controller 40 of this example avoids thatsituation.

The disclosed example also allows for operating an on-site power planteven where there are relatively low inlet gas pressures. Additionally,the disclosed example reduces the number of boosters required andreduces the need to over-design boosters. Further, the disclosed exampleimproves the availability of the prime movers by reducing the tendencyfor a gas booster fault or shutdown to impede operation of the on-sitepower plant.

Another feature of the example controller 40 is that it seeks to providemaximum temperature control capacity within the facility associated withthe on-site power plant 24. In FIG. 1, a building management system 62determines which of the cogeneration units 32, 34 or 36 will be bestsuited to meet a current heating or cooling demand associated with thethermal load 23. The temperature control function in one example is forcontrolling air temperature within a building. Another example includesa temperature control function for managing thermal energy of theon-site power plant 24 or for components of the plant such asinstrumentation or controls. Such temperature control functions may beaccomplished without a building management system 62, for example, andthe thermal load 23 is schematically divided accordingly in theillustration. There are known techniques for making a determinationregarding a desired temperature control function. The example controller40 utilizes such information to set priorities for operating the primemovers to ensure that the best suited cogeneration unit receivesadequate exhaust supply to meet the heating or cooling demand.

For example, if the controller 40 receives information from the buildingmanagement system 62 that the cogeneration unit 34 is best suited tomeet a given need, the controller 40 will prefer to operate the primemovers 28 before operating the prime movers 26 or 30 to ensure that thecogeneration unit 34 receives some exhaust stream. Additionally, in oneexample, the controller 40 prefers to operate at least one prime moverat full capacity more than operating multiple prime movers at less thanfull capacity. Operating a prime mover at full capacity provides higherefficiency in power generation. In one example, this provides theadditional benefit of providing a sufficient exhaust gas stream, forexample, to a cogeneration unit to allow for meeting the demand of thedesired temperature control.

In FIG. 2, at 64, the controller 40 determines the priority of the primemovers based upon the temperature control needs. For building airtemperature control, the controller 40 receives an indication from thebuilding management system 62. For other control functions, thecontroller uses other appropriate indications. The example of FIG. 2contemplates either or both. The controller 40 selects the highestpriority prime mover first to provide the desired power and to enableoperation of the preferred cogeneration unit. This is shown at 66 inFIG. 2.

A significant advantage to the disclosed example is that a controller 40has the ability to adjust the operation of the on-site power plant 24responsive to transients in the power requirements at the electricalload 22. In FIG. 2, at 68, the controller 40 detects transients in thepower draw at the electrical load 22. The controller 40 then determinesthe required power for the electrical load 22 as a result of thetransient. In the event of a down transient, the controller 40determines how much power is required at a lower level compared to acurrent operating level.

Following the example flowchart 42, the result of the inquiry at 52 inthe event of a down transient will be that there are too many primemovers operating for the lower power requirement. Instead of shuttingoff the entire on-site power plant 24, the controller 40 determines at70 how to adjust the operation of the prime movers to respond to thereduced power requirement. In one example, the controller 40 determineshow many of the currently operating prime movers to turn off within therequired power limit. At least one of the prime movers continuesoperating to avoid completely shutting down the on-site power plant 24whenever possible.

Of course, there will be situations when a shutdown of the entire plantis necessary to avoid tripping the relay. One example includes using thecontroller 40 for shutting down under such circumstances to avoid thedrawbacks associated with tripping the relay. Controller-initiatedshutdown allows for faster restart and avoids the negative impact that arelay shutdown may have on the service life of the prime movers.

In one example, the control strategy includes a preference to operateany running prime movers at a full operating capacity. In manyinstances, the controller 40 turns off a number of the prime movers thatresults in a difference in power output from the on-site power plant 24that is greater than the difference between the power draw at the load22 before and after the down transient. In other words, in one example,the controller 40 will turn off a prime mover instead of continuing tooperate it at less than full operating capacity even if that will reducethe power output below the lower level needed as a result of the downtransient. The controller 40 in one example always turns off enough ofthe prime movers so that the difference between the power output fromthe on-site power plant 24 before and after the down transient at theload 22 at least equals the difference in the power draw at the load 22before and after the down transient.

In one example, the controller 40 selects which of the prime movers toturn off taking into account the fuel capacity and cogenerationtemperature control needs as described above. The example strategy shownin FIG. 2 includes a combination of the control techniques for achievingdesired operation of the on-site power plant 24.

The disclosed example provides several advantages compared to previousarrangements. The example controller 40 minimizes the reverse powerexport to the grid responsive to transients in the load requirements ofvirtually any size without requiring the on-site power plant 24 to shutdown. Minimizing power export to the gird minimizes the possibility oftripping a site reverse power protective relay that would otherwisecause the on-site power plant to shut down. This improves theavailability of the on-site power plant and provides better results forthe customer at the facility.

The disclosed example also matches operation of prime movers to therequirements of the cogeneration units to maximize the heating orcooling effect within the facility. This improves system overallefficiency and enhances integration with building management systems.

Although a combination of features are shown in the illustrated example,not all of them need to be combined to realize the benefits of variousembodiments of this invention. In other words, a system designedaccording to an embodiment of this invention will not necessarilyinclude all of the steps shown in FIG. 2 or all of the portionsschematically shown in FIG. 1.

One embodiment uses the example technique for adjusting prime moveroperation without shutting down the entire plant responsive to downtransients. The same example does not include the fuel booster capacityor temperature control monitoring features described above. Anotherexample only includes the fuel capacity-based control technique. Anotherexample combines two of the three. Yet another example only includes thecontrol technique for maximizing temperature control capacity.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this invention. The scope of legal protection given tothis invention can only be determined by studying the following claims.

1. A method of controlling an on-site power plant that has a pluralityof prime movers for generating power, comprising: operating a pluralityof prime movers to generate a first level of power for a load; andadjusting how the prime movers operate responsive to a down transient inthe load while continuing operating at least one of the plurality ofprime movers to generate a second, lower level of power for the load. 2.The method of claim 1, including detecting the down transient in theload; determining an amount of decrease in power required by the loadcorresponding to the detected down transient; and adjusting how theprime movers operate so that the on-site power plant does not providemore power than is required by the load.
 3. The method of claim 2,including determining how many of the prime movers to turn off so that adifference between the first and second levels of power generated by theon-site power plant is at least the determined amount of decrease inpower required by the load.
 4. The method of claim 1, wherein each ofthe prime movers is associated with a cogeneration unit that utilizesexhaust from at least one of the associated prime movers to provide atemperature control function and the method comprises determining whichof the prime movers to turn off responsive to a requirement fortemperature control.
 5. The method of claim 4, wherein the temperaturecontrol is for an air temperature within a building.
 6. The method ofclaim 4, comprising determining which of the cogeneration units ispreferred to meet the requirement for temperature control; and operatingat least one of the prime movers associated with the determinedpreferred cogeneration unit at a higher priority than another primemover associated with another cogeneration unit.
 7. The method of claim6, including operating at least one of the prime movers at full capacityand minimizing a number of the prime movers operating at a lessercapacity.
 8. The method of claim 1, comprising determining a capacityfor fueling the on-site power plant based on an operating condition ofat least one fuel booster; and selectively operating the prime moversresponsive to the determined capacity.
 9. The method of claim 8,comprising turning off at least one of the prime movers responsive todetecting a decrease in the determined capacity while continuing tooperate at least one other of the prime movers.
 10. The method of claim1, comprising selecting which of the plurality of prime movers tooperate such that an amount of power supplied by the on-site power plantis no more than an amount of power required by the load.
 11. An on-sitepower plant, comprising: a plurality of prime movers for generatingpower; and a controller configured to selectively operate the primemovers to generate a first level of power for a load and adjust anoperation of the prime movers responsive to a down transient in the loadwhile continuing to operate at least one of the prime movers to generatea second, lower level of power for the load.
 12. The on-site power plantof claim 11, wherein the controller is configured to detect the downtransient in the load; determine an amount of decrease in power requiredby the load corresponding to the detected down transient; and determinehow many of the prime movers to turn off so that the on-site power plantdoes not provide more power than is required by the load.
 13. Theon-site power plant of claim 12, wherein the controller is configured todetermine how many of the prime movers to turn off so that a differencebetween the first and second levels of power generated by the on-sitepower plant is greater than or equal to the determined amount ofdecrease in power required by the load.
 14. The on-site power plant ofclaim 11, comprising a plurality of cogeneration units, eachcogeneration unit associated with at least one of the prime movers suchthat the cogeneration units use exhaust from an associated prime moverto provide a temperature control; and wherein the controller isconfigured to determine which of the prime movers to turn off responsiveto a requirement for temperature control.
 15. The on-site power plant ofclaim 14, wherein the temperature control is for an air temperaturewithin a building associated with the on-site power plant.
 16. Theon-site power plant of claim 14, comprising a device configured todetermine which of the cogeneration units is preferred to meet therequirement for temperature control, and the controller communicateswith the device, the controller is configured to prioritize operation ofthe prime movers based upon preferring to operate at least one primemover associated with the determined preferred cogeneration unit beforeoperating another prime mover associated with another cogeneration unit.17. The on-site power plant of claim 16, wherein the controller operatesat least one of the prime movers at full capacity.
 18. The on-site powerplant of claim 11, comprising at least one fuel booster that suppliesfuel to the prime movers and wherein the controller is configured todetermine a capacity for fueling the on-site power plant based on anoperating condition of the at least one fuel booster, and the controlleris configured to selectively operate the prime movers responsive to thedetermined capacity.
 19. The on-site power plant of claim 18, whereinthe controller is configured to turn off at least one of the primemovers responsive to detecting a decrease in the determined capacitywhile continuing to operate at least one other of the prime movers. 20.The on-site power plant of claim 11, wherein the controller isconfigured to determine an amount of power supplied to the load by theon-site power plant and an amount of power supplied to the load byanother source of power external to the on-site power plant and thecontroller is configured to select which of the plurality of primemovers to operate such that an amount of power supplied by the on-sitepower plant is no more than an amount of power required by the load. 21.An on-site power plant, comprising: a plurality of prime movers forgenerating power; and a controller that is configured to do at least oneof: control operation of the prime movers to generate a first level ofpower for a load and adjust the operation of the prime movers responsiveto a down transient in the load while continuing to operate at least oneof the prime movers to generate a second, lower level of power for theload; determine which of the prime movers to operate responsive to arequirement for temperature control in a facility associated with theon-site power plant; or determine a capacity for fueling the on-sitepower plant and control operation of the prime movers responsive to thedetermined capacity.
 22. The on-site power plant of claim 19, whereinthe controller is configured to control operation of the prime moverssuch that the on-site power plant provides an amount of power that is nomore than a required amount of power for the load.